<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>align center div</title>
        <style>
            .container {
                width: 600px;
                height: 400px;
                background: steelblue;
                vertical-align: middle;
                display: table-cell;
            }

            .box {
                background: gold;
                width: 100px;
                height: 100px;
                margin: 0 auto;
            }
        </style>
    </head>
    <body>
        <div class="container">
            <div class="box">I am div</div>
        </div>
    </body>
</html>
